The present invention relates generally to a signal reproducing apparatus and relates more particularly to the initialization of a signal reproducing apparatus employing multiple tracks utilizing a stepper motor for moving a transducer from selected track to selected track. Several different types of signal reproducing apparatus presently exist in the prior art. Many of the signal reproducing apparatus utilize a magnetic storage media. One example of a signal reproducing apparatus is a disk drive. Some disk drives utilize a plurality of record tracks per record surface available. Such disk drives may have a single platter with a record surface on one or both sides of the platter or it may employ a plurality of platters employing multiple record surfaces with at least one transducer per record surface and in some cases utilizing a plurality of transducers per single record surface. Another example of a signal reproducing apparatus is that of magnetic tape drives. Again, many of these magnetic tape drives utilize a plurality of record tracks. Still further some of these magnetic tape drives utilizing a plurality of record tracks require that a transducer be moved transverse to the direction of tape movement for the purpose of selecting a particular record track. Still another example of a signal reproducing apparatus employing magnetic media is that of the rotating magnetic drum. Again a magnetic drum may have a plurality of tracks and may have one or more transducers, each of which is responsible for covering a plurality of record tracks on the drum surface. In general, the apparatus of the present invention may be utilized most favorably in conjunction with a signal reproducing apparatus utilizing a magnetic record media having multiple tracks where it is necessary and required that a transducer be moved relative to the record media for the purpose of selecting a particular record track.
When a transducer must be moved relative to a record track, a means of controlling that transducer with respect to the multiple tracks must be achieved. Several methods are used to accomplish this result. One of the simplest examples of moving a transducer relative to a record track involves the use of magnetic tape which has multiple tracks which are offset with respect to the center line of the magnetic tape. The transducer or transducers are then fixed relative to the tape width, and the transducer is moved relative to the record tracks merely by turning the magnetic tape over.
Stepper motors have also been utilized to control transducers with respect to a plurality of record tracks. When the number of record tracks exceeds the number of finite current programs available for the phase windings of the stepper motor, a means is needed for determining the position of the transducer with respect to those record tracks. The device controlling and instructing the stepper motor is able to determine the particular current program currently being applied to the phase windings of the stepper motor, but since there exist more record tracks than finite current programs of the stepper motor, the same current program is utilized repeatedly for more than one record track. One means of maintaining the positional control over the transducer is to utilize multiple transducers controlled by a single stepper motor. The number of transducers is increased to the point where the number of record tracks served by a single transducer is not greater than the number of finite current programs available to the stepper motor then the positioning problems are solved. Still another means is to dedicate one record surface, e.g., one side of a disk platter, to prior encoded data which would identify the particular record track being serviced. Multiple transducers then serving other record services would be mechanically affixed and positioned with respect to the transducer serving the dedicated surface so that the record track being serviced would be readily identifiable. This means, however, is quite wasteful since an entire record surface must be dedicated to the track location information. For example, in a two disk system utilizing four record surfaces, 25% of the usable record media would be wasted due to the necessity of maintaining transducer position information.
However, if the stepper motor was, at start-up, initialized with respect to the record tracks being serviced, then the external device servicing and controlling the transducers and determining which record of track the transducers should service could then keep track of subsequent transducer movement and by updating the position could maintain knowledge of the present position of the transducer or transducers. Such external device is defined as a transducer controller. Such a device is defined as that device which decides and determines which record track the transducer or transducers are to select and to provide the particular current program to be supplied to the phase windings of the stepper motor and to sequence that current program in the phase windings in order to effectively move the stepper motor through a plurality of steps, if necessary, to reach the selected track. Such transducer controllers are well known in the art.
For a specific example, assume that a signal reproducing apparatus has one record media surface. The apparatus has at least one transducer which covers 360 record tracks. Assume that a stepper motor having 8 finite current program states for its phase windings is responsible for controlling the transducer covering those 360 tracks. To illustrate the 8 particular finite current programs, assume that the stepper motor has two phase windings, and also assume that there exist three states for the current in each phase winding. There would then exist three squared, or nine, correct programs for the stepper motor, however, one of those current programs; namely, the one in which zero current is present in each phase winding is a non-preferred step. This current program is therefore eliminated resulting in the stepper motor having 8 finite current programs. In order to cover the 360 record tracks, the stepper motor could go through the 8-step sequence 45 times. When power is initially applied to the signal reproducing apparatus, the transducer controller could supply a particular current program to the stepper motor. The transducer controller would then know which particular step the stepper motor is at but not which of the 45 sequences at which the transducer is located. That is, assume that the transducer controller supplies the current program corresponding to step 8 of the stepper motor, the transducer controller knows that the stepper motor is at step 8 but does not know if the transducer is on track 8, 16, 32 . . . 352 or 360.
However, if the transducer could be initialized so that the transducer controller would know which of the 45 sequences at which the transducer was located then the transducer controlled could then keep track of any subsequent position of the transducer by merely adding and subtracting the record track movement of the transducer. In fact, the transducer controller actually controls the record track movement of the transducer since it (a) should know the current position of the transducer with respect to the record tracks, (b) receives instructions as to the new selected record track to be serviced, (c) by subtracting determines the number of tracks through which the transducer must be moved, and (d) sends a sequence of current programs to the phase windings of the stepper motor to enable the stepper motor to progress in a proper direction a proper number of steps to achieve the new selected record track.